The long-range objective of this research is to investigate the physiological mechanisms of liquid ventilation with the aim of developing a therapeutic method for treating newborn infants with severe respiratory distress such as those with hyaline membrane disease and severe meconium aspiration syndrome. The short-term goal of this study is to evaluate the therapeutic significance and to investigate the physiological mechanisms of ventilating premature lambs with liquid. The proposed research can be grouped as follows: A. A study of basic pulmonary physiological mechanisms such as: (1) In vivo measurement of the dynamic behavior of the liquid ventilated lung. (2) The effect of assisted liquid ventilation on cardiovascular function. (3) In vivo diffusing capacity and the time course of diffusion gradients in the premature liquid-filled lung. B. An evaluation of the therapeutic significance of: (1) liquid lavage (2) short-term liquid ventilation (1 to 4 hours) and (3) intermediate term liquid ventilation (4 to 8 hours) in premature lambs.